<!DOCTYPE html>
<html>
<body>
<p>Text outside the dialog.</p>
<dialog>
  <p>Text in the dialog.</p>
  <iframe srcdoc="
    <p>Text in normal iframe</p>
    <iframe srcdoc='<p>Text in nested normal iframe</p>'></iframe>
  "></iframe>
</dialog>
<iframe srcdoc="
  <p>Text in inert iframe</p>
  <iframe srcdoc='<p>Text in nested inert iframe</p>'></iframe>
"></iframe>
<script>
document.querySelector('dialog').showModal();
</script>
</body>
</html>
